It is recommended that each rider personally or professionally fit themselves to their bicycle
A road bike fit consists of insuring that:
a) There is proper leg extension between the saddle and the pedals. (Do this by having a friend steady your bike, or mount your bike in a stationary trainer with the wheels level. Then place your heels on the pedals and adjust the saddle height so that your legs are fully extended on the downstroke, yet your hips don’t rock as you pedal.)
b) The horizontal tilt of the saddle fits your riding style and integrates with the other fit factors. (You’re going to feel different pressure depending on where you’re resting on the handlebars. Adjust the tilt to be most comfortable in the position that you ride most.)
c) The distance between the saddle and the handlebars is proper. (Check this by placing your hands on the brake hoods and looking down through the center of the handlebar which should obscure the front hub. If the handlebar is ahead of the hub, you are more aerodynamic, and if it’s behind, you should be more comfortable. Adjust bar reach by moving saddle forward or back and/or swapping stems.
d) The height of the handlebars in relation to the saddle provides for the proper angle to minimize shoulder and arm stress. (Set the handlebars lower than saddle height to be more aerodynamic(Very hard to do with any noseless saddle) , and level with or higher than saddle height to be more comfortable.)
Mountain bike: Fit considerations vary for (c) and (d) above. For (c), if the bar is ahead, it’s better for climbing; if it’s behind, it’s better for descending. For (d), having the handlebar higher will assist with technical descents.
Exercise bike: Most exercise bicycles do not allow you to adjust anything other than saddle height. If you can adjust more handlebar distance and height, do so using the guide above.